In a typical packet switched network, each packet contains its own forwarding or routing data (presented differently in almost every OSI layer) that nodes (e.g. routers in the IP layer) between the end points must read in order to make next hop routing decisions. The parts of the forwarding data that is used in forwarding decisions depends both on the transport media and the networking technology. Although there exist solutions to make this forwarding as fast as possible (e.g. GMPLS=Generalized Multi Protocol Label Switching), these tend to operate only after the first few packets have been transmitted and are efficient only for relatively stable configurations between the end points. Even so, routing decisions can only be made once the whole packet, data and routing information, has arrived.
It will be appreciated that circuit switched networks (e.g. PSTN networks) do not have this problem of per packed switching along the data transmission path between the end points, since the path is already determined before transmission. However, circuit switched networks require a more complex signalling architecture in order to create and maintain communication paths, and to and releases network resources when the need for communication between parties ceases to exist.
It is desirable to provide for circuit switched like behaviour across packet switched networks, allowing routing decisions to be made at routing nodes prior to receipt of actual data packets.